This invention relates to a throttle valve control apparatus in an internal combustion engine mounted on a motorcar or the like.
Known throttle valve control apparatuses are often provided with a valve closing means for closing a throttle valve of an engine beyond its idling position. The valve closing means is arranged to operate at the time of deceleration for effecting a decrease in the amount of fuel consumption and improving the fuel cost economy.
It has been usual with this type of apparatus that the valve closing means is controlled in operation by a control means which is responsive to an engine speed signal. The valve closing means is operated at the time of deceleration from such a condition that the engine speed is above a predetermined ON speed, and is released from operation when the engine speed is lowered to a predetermined OFF speed which is near an idling speed thereof, so that the throttle valve is returned to its idling position for preventing the engine speed from lowering below the idling speed. It has been general, in such a case, that the difference between the OFF speed and the ON speed is set to be several 10-100 r.p.m. This is because of the necessary minimum limit of hysteresis required for discrimination of the engine speed sensor. This, however, creates certain inconveniences as described below.
Namely, the actual idling speed provides a dispersion thereof even after adjustment. The upper limit of the adjustment error range thereof is about 400 r.p.m. in relation to a prescribed idling speed required for the engine. For instance, in respect of an engine of which the prescribed idling speed is 650 r.p.m., if the OFF speed thereof is set to be 800 r.p.m. and when the ON speed thereof is set to be 900 r.p.m., having such a hysteresis as described above, it often happens that the set ON speed becomes below the actual idling speed of the engine. Consequently, when, after releasing of the valve closing means from its operation, the throttle valve is returned to its idling position to effect idling, the engine speed rises above the ON speed, and thereby the valve closing means is returned to its operative condition from its released inoperative condition to close the throttle valve again and thereby the engine speed is lowered again to release the valve closing means. In this way, the above operations are repeated to generate such a self-excited vibration as shown by a curve b in FIG. 3. If, in such a case, the OFF speed is set to be near the prescribed idling speed in order to improve the fuel cost economy, the self-excited vibration becomes more remarkable.
This invention has as an object the elimination of any of the above-described self-excited vibrations. This is achieved in an apparatus having a valve closing means for closing a throttle valve of an internal combustion engine beyond an idling position thereof, wherein the valve closing means is controlled in operation by a control means which is responsive to an engine speed and has an engine speed sensor. The valve closing means is operated at the time of deceleration from the condition that the engine speed is above a predetermined ON speed, and is released from operation when the engine speed is lowered to a predetermined OFF speed which is near an idling speed thereof. The invention is characterized in that the ON speed is set to be above an upper limit of an adjustment error range predetermined about the actual idling speed.